Which paper tape hole is bit 1?

Tony Duell ard at p850ug1.demon.co.uk
Fri Nov 18 20:27:22 CST 2005

> Today I was hooking up my homebrewed driver board to the M-series
> connector on the back of my Tally 420PR tape punch (interfaces to
> my 8/A and . Fortunately, before I inserted the eight data pins
> into the connector body it occurred to me that Tally and DEC might
> not interpret the holes in the same order. And indeed they don't!
> The paper tape has five holes on one side of the sprocket hole and
> three on the other. Typical DEC terminology is Bit 1 = MSB and Bit
> 8 = LSB. Is that in fact how DEC labeled it?

Err, that depends on the DEC machine. My PDP11 has bit 0 as the LSB and 
bit 15 asn the MSB. The PDP8/e on my desk has bit 0 as the MSB and bit 
11 as the LSB . I don't know of any DEC machine that has bit 1 as the MSB

> Is the MSB on the outside of the 5-hole side or the 3-hole side?
> Which hole on the tape is which?
MSB                 LSB
   7 6 5 4 3 * 2 1 0

> Even more interestingly, Tally labels their punch pins as follows:
> (* is the sprocket hole)
> 8 7 6 1 2 * 3 4 5

I have an idea that gets 1...5 right for 5-level baudot tape...


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